$spawnable_objects = {}

def can_spawn(spawnable_class)
  $spawnable_objects[spawnable_class.to_s] = spawnable_class
end

can_spawn Wall
can_spawn Turret
can_spawn Crawler

can_spawn Weapon
can_spawn Bullet
can_spawn Rocket
can_spawn LaserBolt

can_spawn WheeledEngine
can_spawn JetEngine

